This invention relates to a process for reforming coal, and more particularly to a method for reforming coal into a form useful for the production of a metallurgical carbonaceous material and/or a liquid product (a liquid fuel, or chemical raw materials) by controlling reaction factors including the residence time distribution of reactants in a reaction zone, except those in gaseous phase, in a predetermined reaction temperature range and under a total reaction pressure, in the "hydrogenation process" in which a slurry mixture containing a low grade coal such as brown coal and a hydrocarbon base solvent is subjected to hydogenation reaction under high temperature and pressure conditions.
To cope with the scarcity and high price in recent years of heavy coking coal, a raw material of coke which is used in iron production, many attempts have thus far been made to produce coke of increased strength from low-grade coals such as brown coal, peat, lignite, some bituminous coal and the like, by the so-called coal liquefaction technology (involving the hydrogenation reaction either in one step or in two steps), which produces a liquid product from coals, producing a solvent-refined coal by hydrogenation reaction of low-grade coals and blending it into a raw material to be used for coke production. In this connection, Japanese Laid-Open Patent Specification Nos. 67801/75 and 27894/76 disclose related processes: the former is directed to a process consisting of hydrogenating a noncoking or coking coal with a hydrocarbon solvent in a pressurized hydrogen atmosphere, separating solid fractions, and blending desulfurized and deashed, highly flowable products having a melting point of 100.degree. C. to 350.degree. C. into the raw coal to be coked; and the latter is directed to a process consisting of bringing an oxygen-rich solid carbonaceous fossil fuel, which is unsuitable for coking, into contact with a solvent and hydrogen for deoxygenation under pressurized and heated conditions, removing the solvent and volatile components from the resulting mixture by distillation, and recovering the residual mixture which can be used as a blending material for coke making. The latter process is especially advantageous since it dispenses with the deashing step which has been essential in the conventional coal liquefaction technology.
It is also known in the art to obtain a liquid product by further deashing and secondarily hydrogenating the solvent refined coal which is obtained by the above-mentioned process.
However, in the prior art including the above-mentioned processes, the hydrogenation step itself still depends on the conventional coal liquefaction technology, leaving many problems unsolved in obtaining carbonaceous products of a quality suitable for use as a metallurgical carbonaceous material, including coke for iron production. More particularly, when hydrogenating low-grade coals such as brown coal, peat, lignite, some bituminous coals and the like to obtain coke for steel production, the most important technical problem is how to improve the strength of coke of the ultimate product. This problem was not considered in the conventional coal liquefaction technology, and therefore the relation between the conditions of the hydrogenation reaction and the quality of the solvent refined coal as a metallurgical carbonaceous material has been unknown to date. In other words, there have not yet been developed processes which are capable of producing solvent refined coal of commercially satisfactory quality in an assured manner.
On the other hand, when a solvent-refined coal which is an intermediate product in the above-mentioned conventional processes is further subjected to secondary hydrogenation after separation by reduced pressure distillation for the purpose of obtaining a liquid product, the so-called coking trouble is often experienced at the bottom of the distillation tower due to free radicals or other unstable substances which remain in large amounts in the intermediate product depending upon the conditions of the primary hydrogenation. In addition, where such unstable solvent refined coal is subjected to secondary hydrogenation, difficulties are also encountered in that the increase in viscosity of the reaction mixture makes the deashing step troublesome, and said free radicals or other unstable substances invite deterioration of catalyst in the succeeding hydrogenation step due to coke deposition on the hydrogenation catalyst. However, no clarification has ever been made with regard to the relation between the reaction conditions of the primary hydrogenation step and the content of unstable substances in the solvent refined coal, and there has been proposed no method effective for reducing the content of the unstable substances.